JPH11293182A - Coating material for precoated steel plate excellent in weatherability, surface hardness and stain resistance, precoated steel plate, and its production and use - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prepare a coating material for precoated steel plate, using a low-priced polyacrylic resin and giving better weatherability, surface hardness and stain resistance, and to provide a precoated steel plate and panels for roof walls, outdoor advertisement, illumination reflection, interior finish for tunnels, the exterior of a car, a partition, interior finish for an elevator, and to provide a method for producing the precoated steel plate. SOLUTION: This coating material is prepared by including both (A) an acrylic polyol-based copolymer resin obtained form a polymerizable monomer for stabilization to ultraviolet light, a polymerizable monomer having a cycloalkyl group and a polymerizable monomer having hydroxyl group as essential monomers and (B) a compound having a siloxane skeleton and a number average molecular weight of <=3,500 as essential components (wherein, the component B is included in a quantity of 0.1-10.0 pts.wt. based on 100 pts.wt. of the total of dried coated film except the component B, i.e., in terms of the outage ratio). The coating material is applied to at least one surface of steel plate or various panels and is made film to produce precoated steel plate and panels. The coating material is applied in a coating thickness of 1-25 μm and then is baked in the plate temperature of range from 150 deg.C to 320 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a paint for a pre-coated steel sheet and a pre-coated steel sheet which are excellent in weather resistance and stain resistance and are used for home appliances, building materials, automobiles and the like.

[0002]

2. Description of the Related Art Generally, thin steel sheet products are used after being painted. The purpose of this coating is to protect the base steel plate and at the same time to increase its durability and beautify it. Painted steel sheets are used for everything from large structures such as buildings, ships, bridges, etc. to various machines, automobiles, furniture, small appliances and household goods, but the painting of these steel sheets is generally called post-coating. Performed after processing and assembly.
However, in the field of building materials and home appliances, there is a shift to a method of processing and assembling a so-called pre-coated steel sheet which has been painted in advance. In this precoated steel sheet, a polymerized resin having processability is used for the coating layer so that the coating film does not peel off during processing. In particular, when a polyacryl resin is used for the coating layer, a beautiful appearance can be obtained.

[0003]

However, when a pre-coated steel sheet using a polyacrylic resin paint is used outdoors or the like, there may be a problem in appearance defects due to contamination by rain and wind or dust. Furthermore, in the case of polyacrylic resin, sufficient weather resistance cannot be obtained. In addition, weather resistance refers to durability performance against a change in appearance due to deterioration or deterioration of resin due to irradiation of sunlight or wind and rain when using a precoated steel sheet outdoors.

[0004] The present invention has been made in order to solve the aforementioned problems.
Precoat having good surface hardness, stain resistance and weather resistance by essentially containing a copolymerized acrylic polyol resin having excellent weather resistance and a compound having a siloxane skeleton and having a number average molecular weight of 3500 or less. Paint for coated steel sheet, and precoated steel sheet used for coating layer and method for producing the same,
Another object of the present invention is to provide an application using the precoated steel sheet of the present invention.

[0005]

SUMMARY OF THE INVENTION A paint for a coated steel sheet and a coated steel sheet according to the present invention, which achieve the above-mentioned objects, comprise a polymerizable ultraviolet-stable monomer, a cycloalkyl group-containing polymerizable monomer. Body, a copolymerized acrylic polyol resin obtained by copolymerizing a polymerizable monomer component essentially containing a hydroxyl group-containing polymerizable monomer, and a compound having a siloxane skeleton having a number average molecular weight of 3500 or less, a coating composition and It is characterized by having in a coating layer.

The prepainted steel sheet of the present invention is used for roof walls,
Use in panels for outdoor advertising, lighting reflection, tunnel interiors, automobile exteriors, partitions, elevator interiors, etc. to obtain thin steel sheet products with excellent weather resistance, surface hardness and stain resistance. be able to.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the paint for precoated steel sheet of the present invention will be described in more detail. The paint for a steel sheet coated with a precoat of the present invention comprises a copolymerized acrylic polyol resin containing a polymer component for improving weather resistance and a compound having a siloxane skeleton.

[0008] Copolymerized acrylic polyol resins include a polymerizable UV-stable monomer containing a functional group such as a hindered amine having UV-stabilizing ability, and a coating film having sufficient durability without deteriorating the weather resistance of the resin. It is essential to include a cycloalkyl group-containing polymerizable monomer that maintains the properties, an improvement in substrate adhesion, and a hydroxyl group-containing polymerizable monomer that can be a crosslinking point in the presence of a crosslinking agent.

The polymerizable UV-stable monomer is an essential compound for imparting excellent weatherability to the copolymer, and particularly includes at least a sterically hindered piperidinyl group and a polymerizable unsaturated group in the molecule. One having one is awarded, and among them, the substance represented by the formula (1) is most typically used.

[0010]

Embedded image

Here, R ¹ is a hydrogen atom or a cyano group,
R ² and R ³ each independently represent a hydrogen atom or carbon atom 1
X is an imino group or an oxygen atom; Y is a hydrogen atom or an alkyl group having 1 to 18 carbon atoms or -C
Shows the O-CR ² = CHR ^3. Exemplarily, by giving specific compound names, for example, 4- (meth) acryloyloxy-2,2,6,6-tetramethylpiperidine,
-(Meth) acryloylamino-2,2,6,6-tetramethylpiperidine, 4- (meth) acryloyloxy-1,2,
2,6,6-pentamethylpiperidine, 4- (meth) acryloylamino-1,2,2,6,6-pentamethylpiperidine,
4-cyano-4- (meth) acryloylamino-2,2,6,
6-tetramethylpiperidine, 1- (meth) acryloyl-4- (meth) acryloylamino-2,2,6,6-tetramethylpiperidine, 4-crotonoyloxy-2,2,6,
Examples thereof include 6-tetramethylpiperidine and 1-crotonoyloxy-2,2,6,6-tetramethylpiperidine, and one or more of these can be used.

The cycloalkyl group-containing polymerizable monomer is an essential compound for maintaining the durability of the coating film without deteriorating the weather resistance of the resin, and is a compound represented by the formula (2): Is most typically used.

[0013]

Embedded image

Here, R ⁴ in the formula (2) represents a hydrogen atom or an alkyl group having 1 to 2 carbon atoms, and Z represents a cycloalkyl group which may have a substituent. Explaining concretely by giving specific compound names, for example, cyclohexyl (meth) acrylate, methylcyclohexyl (meth) acrylate
And tert-butylcyclohexyl (meth) acrylate, and one or more of these can be used.

Next, examples of the hydroxyl group-containing polymerizable monomer include hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, and caprolactone-modified hydroxy (meth) acrylate. , One or more of these can be used. Further, as other polymerizable monomers, for example,
Methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl (meth) acrylate, t-butyl (meth) acrylate
(Meth) acrylic acid alkyl esters such as 2-ethylhexyl (meth) acrylate and epoxy group-containing unsaturated monomers such as glycidyl (meth) acrylate;
Nitrogen-containing unsaturated monomers such as (meth) acrylimide, N, N'-dimethylaminoethyl (meth) acrylate, vinylpyridine, vinylimidazole, styrene, α
-Aromatic unsaturated monomers such as methylstyrene and vinyltoluene; vinyl esters such as vinyl acetate;
Examples thereof include unsaturated cyanide compounds such as ter and (meth) acrylonitrile, and one or more of these can be used as needed.

The copolymerization of the above-mentioned polymerizable monomer components is not particularly limited, but the content ratio of each monomer component is preferably from 0.1 to 10.0 of the UV-stable polymerizable monomer. % By weight, cycloalkyl group-containing polymerizable monomer 5.0 to 9
7.9% by weight, hydroxyl group-containing polymerizable monomer 2.0 to 35.
0% by weight and 0 to 92.9% by weight of the other polymerizable monomers in the range of 100% by weight of the copolymerized acrylic polyol resin.
It is preferred that it constitutes% by weight.

Next, the compound having a siloxane skeleton will be described. Siloxane is a general term for compounds containing Si—O—Si bonds, and the general formula is H ₃ SiO— (H ₂ S
iO) represented by _n -SiH _3. The compounds having a siloxane skeleton used in the present invention are various substitution products of this siloxane, and generally refer to those called silicon resins and silicone oils.

It is essential that the number average molecular weight of this compound is 3500 or less. When a compound having a molecular weight higher than this is mixed with the above-mentioned copolymerized acrylic polyol resin, incompatibility or gelation occurs, so that it does not form a body as a paint, and sufficient surface hardness for the coating layer. Can not be given. The molecular weight distribution state of the compound is not particularly defined.

There are no particular restrictions on the types of substituents of the various substituents of this compound. Carbonyl group or hydroxyl group,
Modification with an organic group such as an ether group or an alkyl group or an inorganic group such as titanic acid or molybdic acid is appropriately performed to control the compatibility with the copolymerized acrylic polyol resin and the self-shrinkage property at the time of firing the coating layer. Can be done. Further, the molecular length and configuration of the compound such as a straight chain or a subchain may be appropriately combined and used.

The compounding ratio of this compound to the copolymerized acrylic polyol resin is required to be 0.1 to 10.0 parts by weight based on an external ratio of 100 parts by weight of the whole dry coating film excluding this compound. It is. If the amount is less than 0.1 part by weight, sufficient stain resistance and surface hardness cannot be given to the coating layer, and
If it is added in an amount of more than 0.0 parts by weight, an incompatible layer of only the compound is formed in the coating layer, and the contamination resistance of the coating layer tends to decrease.

The method of mixing the copolymerized acrylic polyol resin and the compound is not particularly limited. What is necessary is just to mix until it is dispersed, compatible or turbid by a general method used at the time of compounding the paint. In addition, a crosslinking agent can be added to the paint as needed. As a crosslinking agent, an aminoplast resin or a polyisocyanate compound can be used alone or in combination.

Examples of the aminoplast resin include a methyletherified melamine resin, a butyletherified melamine resin, a butyletherified benzoguanamine resin, and a butyletherified cyclohexylbenzoguanamine resin. The mixing ratio of the aminoplast resin to the copolymer acrylic polyol resin is 10 to 10 parts by weight based on 100 parts by weight of the copolymer acrylic polyol resin.
It is preferably 0 parts by weight.

Further, as the polyisocyanate compound,
As long as the molecule contains two or more isocyanate groups, for example, trimethylene diisocyanate, 1.6-hexamethylene diisocyanate, tolylene diisocyanate, diphenylmethane diisocyanate , Isophorone diisocyanate, and trimethylolpropane adducts which are derivatives of these diisocyanates;
Adduct polyisocyanate compounds such as ret-forms and isocyanurate-forms. Further, the isocyanate group of the isocyanate compound may be ε-caprolactam, phenol, cresol, oxime, or alcohol. And a blocked polyisocyanate compound blocked with a compound such as The mixing ratio of the polyisocyanate compound to the acrylic polyol resin is such that the isocyanate group is 0.3 to 2.0 mol per 1 mol of the OH group of the copolymerized acrylic polyol resin. It is suitable.

When using a curing agent, a curing catalyst such as dodecylbenzenesulfonic acid (DBSO) may be added as necessary. The compounding amount may be appropriately determined according to the expected firing conditions and the balance of the coating film performance. Furthermore, titanium pigments such as titanium white pigment, titanium yellow, carbon black, etc., extender pigments such as silica, amphoteric surfactants, leveling effect agents, antioxidants, ultraviolet absorbers, etc., are generally used in paints. If necessary, these additives may be used by mixing them in necessary amounts.

Particularly, in order to improve the weather resistance, it is effective to use an additive capable of absorbing light at a specific wavelength. As an example, the use of a benzotriazole-based or oxalic anilide-based ultraviolet absorber in the coating makes it possible to achieve a wavelength of 200 nm.
It is possible to improve the weather resistance performance in an accelerated weather resistance test using a germicidal lamp or the like having a strong line in a region of up to 220 nm as a light source.

There is no particular limitation on the composition of the diluting solvent. In general, any solvent may be used as long as it is a diluting solvent generally used for paints for pre-coated steel sheets.
Next, the precoated steel sheet of the present invention will be described in detail. The pre-coated steel sheet is composed of a steel sheet and a coating layer. As the base steel sheet, cold-rolled steel sheet, hot-rolled steel sheet, galvanized steel sheet, alloyed galvanized steel sheet, zinc-iron alloy coated steel sheet, zinc-aluminum alloy coated steel sheet, aluminum-plated steel sheet, chrome-plated steel sheet, nickel-plated Examples include a steel sheet, a zinc-nickel alloy-plated steel sheet, a tin-plated steel sheet, a stainless steel sheet, an aluminum-plated stainless steel sheet, a lead-plated stainless steel sheet, and a zinc-plated stainless steel sheet.

[0027] The steel sheet may be subjected to a pretreatment as required. Examples of pretreatment include washing with water, washing with hot water, pickling, alkali degreasing, grinding, polishing, chromate treatment, zinc phosphate treatment, composite oxide film treatment, etc. Good. Conditions for each pretreatment may be appropriately selected. Next, the coating layer applied to at least one surface of the steel sheet is composed of a mixture essentially containing the above-mentioned copolymerized acrylic polyol resin and a compound having a siloxane skeleton.

It is essential that the copolymerized acrylic polyol resin contains a unit based on the aforementioned polymerizable ultraviolet light-stable monomer, cycloalkyl group-containing polymerizable monomer, and hydroxyl group-containing polymerizable monomer. And The content and the mixing ratio of each polymerizable monomer are the same as those described above. The compound having a siloxane skeleton has a number average molecular weight of 35.
Various substitution products of siloxane having a value of 00 or less are used. The contents such as the types of the substituents are the same as those described above.

The amount of the compound to be added is desirably 0.1 to 10.0 parts by weight in terms of an outer ratio of 100 parts by weight of the whole dry coating film excluding the compound. When the addition amount is less than 0.1 part by weight, sufficient stain resistance and surface hardness cannot be obtained, and when the addition amount is larger than 10.0 parts by weight, the immiscible layer of the siloxane compound is not contained in the coating layer. Generate
The stain resistance of the coating layer is reduced.

Further, a crosslinking agent can be used in the coating layer, if necessary. As a crosslinking agent, an aminoplast resin or a polyisocyanate compound can be used alone or in combination. The type, composition and compounding method of each crosslinking agent,
The presence or absence of a curing catalyst is the same as described above. Further, general precoat coating such as color pigments such as titanium white pigment, titanium yellow and carbon black, extender pigments such as silica, amphoteric surfactants and leveling effect agents, antioxidants and ultraviolet absorbers. As long as it is an additive used for a steel sheet, it may be used by appropriately mixing them in a necessary amount.

Particularly, in order to improve the weather resistance, it is effective to use an additive capable of absorbing light at a specific wavelength. As an example, the use of a benzotriazole-based or oxalic anilide-based ultraviolet absorber in the coating makes it possible to achieve a wavelength of 200 nm.
It is possible to improve the weather resistance performance in an accelerated weather resistance test using a germicidal lamp or the like having a strong line in a region of up to 220 nm as a light source.

As for the film thickness of the coating layer, it is necessary to set the dry film thickness to 1 to 25 μm from the viewpoint of ensuring workability and workability of coating. When the thickness is less than 1 μm, abnormal appearance during coating such as omission tends to occur, and when the thickness is more than 25 μm, the processing adhesion to the base material is poor, and the coating film in the processed portion may be peeled off. In addition, a single layer or a plurality of organic coating layers may be formed between the steel sheet and the coating layer as necessary. Regarding the provided organic coating layer, there is no limitation on the use of the additive component generally used for the pre-coated steel sheet. Examples thereof include color pigments, extender pigments, rust preventive pigments and dyes, leveling components, and design components such as metallic, mica, and aggregate.

The thickness of each organic coating layer is not specifically defined, but is preferably 25 μm or less in view of the drying limit in the manufacturing process and the workability of the coating layer. 25μ
When the film thickness is larger than m, the coating film may peel off during processing. Next, the method for producing the precoated steel sheet of the present invention will be described in detail. First, as the coating layer in the present invention, the above-mentioned copolymer acrylic polyol was used.
It is composed of a paint containing a resin having a siloxane skeleton and a compound having a siloxane skeleton.

It is essential that the copolymerized acrylic polyol resin contains a unit based on the aforementioned polymerizable ultraviolet light-stable monomer, cycloalkyl group-containing polymerizable monomer, and hydroxyl group-containing polymerizable monomer. And The content and the mixing ratio of each polymerizable monomer are the same as those described above. The compound having a siloxane skeleton has a number average molecular weight of 35.
Various substitution products of siloxane having a value of 00 or less are used. The contents such as the types of the substituents are the same as those described above.

With respect to the amount of the compound,
It is desirable that the amount is 0.1 to 10.0 parts by weight based on 0 parts by weight. When the addition amount is less than 0.1 part by weight, sufficient stain resistance and surface hardness cannot be obtained, and when the addition amount is larger than 10.0 parts by weight, the immiscible layer of the siloxane compound is not contained in the coating layer. It forms and reduces the contamination resistance of the coating layer. In addition, a crosslinking agent can be used in the paint if necessary. As a crosslinking agent, an aminoplast resin or a polyisocyanate compound can be used alone or in combination. The type, composition and compounding method of each crosslinking agent, and the presence or absence of a curing catalyst are the same as those described above.

Further, color pigments such as titanium white pigment, titanium yellow and carbon black, extender pigments such as silica, amphoteric surfactants and leveling effect agents, antioxidants,
If it is an additive such as an ultraviolet absorber used in general pre-coated steel sheet, it may be used by appropriately mixing them in necessary amounts. In particular, in order to improve the weather resistance performance, the use of an additive having an absorption capacity at a specific wavelength is effective. For example, by using a benzotriazole-based or oxalic acid anilide-based ultraviolet absorber in a coating, a wavelength of 200 to
The weather resistance performance in an accelerated weather resistance test using a germicidal lamp or the like having a strong line in a 220 nm region as a light source can be improved.

The paint is applied on at least one side of the steel sheet so that the dry film thickness is 1 to 25 μm. 1μ coating thickness
If it is less than m, poor appearance such as color omission or insufficient weather resistance occurs. On the other hand, if it exceeds 25 μm, workability will be insufficient. After application, baking is performed at 150 ° C. or more and less than 320 ° C., and curing and drying are performed. If the baking temperature is lower than 150 ° C., the solvent used in the coating material does not sufficiently evaporate, resulting in insufficient curing of the coating film. If the baking temperature is higher than 320 ° C., the resin component deteriorates due to heat and the workability is deteriorated.

As a method of applying the coating, a roll coater, a curtain flow coater, a roller curtain coater, an electrostatic coating machine, a brush, a blade coater, a die coater or the like is used to apply a coating to a required film thickness. The subsequent curing and drying method is preferably drying at room temperature or in a hot-air oven, induction heating oven, near-infrared oven, far-infrared oven, energy ray curing oven, or the like.

The steel sheets include cold-rolled steel sheets, hot-rolled steel sheets, galvanized steel sheets, galvannealed steel sheets, zinc-iron alloy coated steel sheets, zinc-aluminum alloy coated steel sheets, aluminized steel sheets, chromium-coated steel sheets, nickel Plated steel sheet,
Examples include a zinc-nickel alloy-plated steel sheet, a tin-plated steel sheet, a stainless steel sheet, an aluminum-plated stainless steel sheet, a lead-plated stainless steel sheet, and a zinc-plated stainless steel sheet.

Further, a pretreatment can be applied to the steel sheet as required. Examples of pretreatment include washing with water, washing with hot water, pickling, alkali degreasing, grinding, polishing, chromate treatment, zinc phosphate treatment, composite oxide film treatment, etc. Good. Conditions for each pretreatment may be appropriately selected. Further, a single layer or a plurality of organic coating layers may be formed between the steel sheet and the coating layer, if necessary. Regarding the provided organic coating layer, there is no limitation on the use of the additive component generally used for the pre-coated steel sheet. Examples include color pigments and extender pigments, rust-preventive pigments and dyes,
Examples include leveling components and design components such as metallic, mica, and aggregates.

The thickness of each organic coating layer is not particularly limited, but is preferably 25.0 μm or less in view of the drying limit in the manufacturing process and the processability of the coating layer. When the film thickness is larger than that, there is a possibility that the coating film in the processed portion may peel off when the product is processed. The above-mentioned precoated steel sheet of the present invention is, for example, a panel for a roof wall, a panel for an outdoor advertisement, a panel for lighting reflection, a panel for a tunnel interior, a panel for an automobile exterior, a partition panel, an elevator interior panel, and the like. By applying to parts exposed to the outdoor atmosphere, it is possible to obtain a thin steel plate product excellent in weather resistance, surface hardness and stain resistance.

[0042]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the paint for a pre-coated steel sheet, the pre-coated steel sheet and the method for producing the same according to the present invention will be described. The coating materials shown in Table 1 were applied on a hot-dip galvanized steel sheet subjected to alkali degreasing and chromate treatment using a bar coater, and then baked by a high frequency induction heating method.

The obtained pre-coated steel sheet was evaluated for weather resistance, stain resistance and surface hardness under the following conditions. Weather resistance: As an accelerated weather resistance test, a sunshine weather meter (SWOM) was used to measure and evaluate a chromaticity difference (ΔE) and a gloss retention (GR) before and after the test for 3000 hours. Stain resistance: As an accelerated stain resistance test, a test material was immersed in a 5% carbon black solution for 200 hours, and the chromaticity difference (ΔE) between after taking out and washing and before starting the test was measured and evaluated. Surface hardness: As a surface hardness measurement test, a fracture value was measured and evaluated by a pencil hardness test.

Table 2 shows the test results. Note that the chromaticity difference (ΔE) is measured using a chromaticity measuring device, and ΔE is 1.0
The following were judged to be good. The gloss retention (GR) was measured with a 60-degree reflectometer, and 60% or more was judged to be good. The surface hardness was determined to be good when the pencil hardness destruction value was 2H or more. As is clear from Table 2, the pre-copper according to the present invention was used.
It can be seen that the paint for steel coated steel sheet and the pre-coated steel sheet show excellent weather resistance, surface hardness and stain resistance when the polymer composition and the compounding ratio, the film thickness and the baking temperature are within appropriate ranges.

[0045]

[Table 1]

[0046]

[Table 2]

Further, the precoated steel sheet of the present invention shown in Table 1 was used for roof wall panels, outdoor advertising panels, lighting reflection panels, tunnel interior panels, automobile exterior panels, partition panels, elevators. As a result of examining the weather resistance, the surface hardness, and the stain resistance when applied to the interior panel, the same weather resistance, surface hardness, and stain resistance as those in Table 2 were exhibited.

[0048]

According to the present invention, a polymerizable ultraviolet-stable monomer,
Preco-containing essentially a cycloalkyl group-containing polymerizable monomer, an acrylic polyol resin obtained by copolymerizing a hydroxyl group-containing polymerizable monomer, and a compound having a siloxane skeleton.
By using the paint for coated steel sheet, the pre-coated steel sheet, and the method of manufacturing the same, it is possible to manufacture a thin steel sheet product excellent in weather resistance, surface hardness and stain resistance, and to reduce the product cost.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI C09D 183/04 C09D 183/04 (72) Inventor Ryoji Nishioka 1 Kimitsu, Kimitsu-shi, Chiba Prefecture Nippon Steel Corporation Kimitsu Works (72) Inventor Masashi Takasugi 1 Kimitsu, Kimitsu City, Chiba Prefecture Inside Kimitsu Works, Nippon Steel Corporation (72) Inventor ▲ Yoshi ▼ Masaya 5-8 Nisomitabi-cho, Suita-shi, Osaka Japan Catalyst Co., Ltd. (72) Inventor Takao Minami 5-8 Nishiburi-cho, Suita-shi, Osaka, Japan Inside Nippon Shokubai Co., Ltd.

Claims (15)

[Claims] 1. A copolymer obtained by copolymerizing a polymerizable monomer component essentially containing a polymerizable ultraviolet-stable monomer, a cycloalkyl group-containing polymerizable monomer, and a hydroxyl group-containing polymerizable monomer. A compound having an acrylic polyol resin as a main component and having a siloxane skeleton and having a number average molecular weight of 3500 or less is contained in an outside ratio of 0.1 to 10.0 parts by weight based on 100 parts by weight of the entire dry coating film excluding the compound. A paint for a pre-coated steel sheet having excellent weather resistance, surface hardness and stain resistance after film formation. 2. A polymerizable monomer component essentially containing a polymerizable UV-stable monomer, a cycloalkyl group-containing polymerizable monomer, and a hydroxyl group-containing polymerizable monomer on at least one surface of a steel sheet. Having a number average molecular weight of 35 having a siloxane skeleton and a copolymerized acrylic polyol resin obtained as a main component.
It has a coating layer having a dry film thickness of 1 to 25 μm, which contains a compound of not more than 00 and a dry film thickness of 0.1 to 10.0 parts by weight based on an external ratio of 100 parts by weight of the whole dry coating film excluding the compound. Precoated steel sheet excellent in weather resistance, surface hardness and stain resistance. 3. A copolymer obtained by copolymerizing a polymerizable monomer component essentially containing a polymerizable ultraviolet-stable monomer, a cycloalkyl group-containing polymerizable monomer, and a hydroxyl group-containing polymerizable monomer. A compound having an acrylic polyol resin as a main component and having a siloxane skeleton and having a number average molecular weight of 3500 or less is contained in an outside ratio of 0.1 to 10.0 parts by weight based on 100 parts by weight of the entire dry coating film excluding the compound. Precoat coating excellent in weather resistance, surface hardness and stain resistance, characterized in that a paint is applied on at least one side of a steel sheet in a dry film thickness of 1 to 25 µm and then fired at a plate temperature of 150 to 320 ° C. Steel plate manufacturing method. 4. The polymerizable UV-stable monomer is represented by the formula (1):[However, R in the formula (1)¹Is a hydrogen atom or a cyano group, R
^Two, R^ThreeAre each independently a hydrogen atom or a carbon number 1 to
X is an imino group or an oxygen atom, Y is water
An atom or an alkyl group having 1 to 18 carbon atoms or -CO
-CR^Two= CHR ^Three(Where R^Two, R^ThreeIs the same as before)
Is shown. The weather resistance according to claim 1, 2 or 3, which is represented by the following formula:
Coated steel sheet with excellent heat resistance, surface hardness and stain resistance
Paint or pre-coated steel sheet or method for producing the same. 5. The cycloalkyl group-containing polymerizable monomer has a formula
(2) [However, R ⁴ in the formula (2) is a hydrogen atom or a carbon atom having 1 to 2 carbon atoms.
And Z represents a cycloalkyl group which may have a substituent. The paint, precoated steel sheet or method for producing a coated steel sheet having excellent weather resistance, surface hardness and stain resistance according to claim 1, 2, 3 or 4. 6. A coating composition and a coating layer, wherein an aminoplast resin and / or a polyisocyanate compound is used as a crosslinking agent component.
Or a paint for a pre-coated steel sheet or a pre-coated steel sheet having excellent weather resistance, surface hardness and stain resistance described in 5 or a method for producing the same. 7. A prepreg having excellent weather resistance, surface hardness and stain resistance according to claim 2, wherein a chemical conversion treatment layer is provided between the coating layer and the steel sheet. Coated steel sheet or its manufacturing method. 8. The weather resistance as claimed in claim 2, wherein an organic coating layer is applied between the coating layer and the steel sheet and / or on the coating layer. A precoated steel sheet having excellent surface hardness and stain resistance, or a method for producing the same. 9. A roof wall panel using the pre-coated steel sheet according to claim 2. Description: 10. An outdoor advertising panel using the precoated steel sheet according to claim 2. Description: 11. A lighting reflection panel using the precoated steel sheet according to claim 2. Description: 12. A panel for a tunnel interior using the precoated steel sheet according to any one of claims 2 to 8. 13. An automotive exterior panel using the precoated steel sheet according to claim 2. Description: 14. A partition panel using the precoated steel sheet according to claim 2. Description: 15. An elevator interior panel using the precoated steel sheet according to claim 2. Description: